A solid-state imaging device such as a CCD image sensor and a complementary metal oxide semiconductor (CMOS) image sensor which are used in a video camera and a digital still camera accumulates charges according to an amount of incident light therein, and performs photoelectric conversion to output an electric signal corresponding to the accumulated charges. A color filter is installed in each imaging device in order to individually accumulate a specific wavelength, that is, a signal corresponding to a specific color, per each pixel unit. For example, a filter having a Bayer array configured to include each color of RGB is frequently used.
On the other hand, in recent years, a miniaturized and pixel-increased imaging device causes a pixel to progressively become hyperfine. The imaging device having this high density pixel is essential to capture a high resolution image.
However, there is a problem in that the imaging device having this high density pixel can accumulate fewer charge amounts per one pixel, thereby relatively increasing a noise amount included in each pixel signal.
Furthermore, for example, PTL 1 (Japanese Unexamined Patent Application Publication No. 2006-253876) has proposed a configuration in which a high dynamic range image is generated by changing the exposure time for each pixel unit by using the imaging device having the high density pixel, by simultaneously acquiring a long-period exposure image and a short-period exposure image, and by synthesizing multiple images whose exposure periods are different from each other.
An imaging method according to this technique has a problem in that when any pixel in the long-period exposure and the short-period exposure cannot be effectively used, the noise amount relatively increases as compared to the technique in the related art. For example, in a case of a dark scene, the noise amount of the short-period exposure image increases, and thus, the image is generated by using only the long-period exposure image. In this case, the image is generated by using only half of the pixels as compared to the technique in the related art, thereby resulting in degraded resolution or increased noise.
PTL 2 (Japanese Unexamined Patent Application Publication No. 2004-304706) and PTL 3 (U.S. Patent Application Publication No. 2007/0024879) have proposed an imaging device configuration having an RGBW array in which a white (W) pixel transmitting whole wavelength light is added to an RGB array, in order to increase a charge accumulation amount for each pixel.
The charge accumulation amount for each pixel is increased by setting the W pixel in addition to the RGB, thereby reducing the relative noise amount included in the pixel signal.
However, the RGBW array disclosed in these PTLs is configured so that if the W pixel is added thereto, pixel density of the other color pixels is considerably degraded. Specifically, in a case of the R pixel or the B pixel, only one pixel exists in every eight pixels. Therefore, a problem arises in that color resolution is degraded, color noise is increased, and an image quality is degraded.
Even if the configurations disclosed in PTLs 1, 2 and 3 are combined with one another, the color resolution is degraded and the color noise is increased. No configuration can solve the problem of the degraded color resolution and the increased color noise which result from low pixel density, since only one pixel exists in every 16 pixels in a case of the R pixel and the B pixel in the long-period exposure and the R pixel and the B pixel in the short-period exposure.